COMPARISON OF SMOOTH COMPARISON OF SMOOTH MUSCLE CONTRACTION AND MUSCLE CONTRACTION AND

SKELETAL MUSCLE SKELETAL MUSCLE CONTRACTIONCONTRACTION

Detailed comparisonDetailed comparison

ENERGY REQUIRED TO SUSTAIN ENERGY REQUIRED TO SUSTAIN SMOOTH MUSCLE CONTRACTIONSMOOTH MUSCLE CONTRACTION

Frequency is 1/10 to 1/300 energy is Frequency is 1/10 to 1/300 energy is required to sustain the same tension of required to sustain the same tension of contraction is smooth muscle as in skeletal contraction is smooth muscle as in skeletal musclemuscleOnly one ATP is required for whole cycleOnly one ATP is required for whole cycle

Skeletal musclesSkeletal musclesRapid contraction and Rapid contraction and relaxation in skeletal relaxation in skeletal musclesmusclesRapidity of cyclingRapidity of cyclingFraction of time is greaterFraction of time is greaterGreater activity of Greater activity of ATPaseATPaseRapid cycling and Rapid cycling and degradationdegradation

Smooth musclesSmooth musclesSmooth muscle Smooth muscle contraction is prolongedcontraction is prolonged

Slowness of cyclingSlowness of cycling\\Much much slowerMuch much slowerFar less ATPase activityFar less ATPase activity

Slow cyclingSlow cycling

COMPARISON OF SMOOTH MUSCLE COMPARISON OF SMOOTH MUSCLE CONTRACTION AND SKELETAL MUSCLE CONTRACTION AND SKELETAL MUSCLE

CONTRACTIONCONTRACTION

Energy required to sustain Energy required to sustain smooth muscle contractionsmooth muscle contraction

Skeletal musclesSkeletal muscles1/101/10

Smooth musclesSmooth muscles1/3001/300One ATP for one cycleOne ATP for one cycle

SLOWNESS OF ONSET OF SLOWNESS OF ONSET OF CONTRACTION AND RELAXATION OF CONTRACTION AND RELAXATION OF

THE SMOOTH MUSCLE TISSUETHE SMOOTH MUSCLE TISSUETime for contraction after excitationTime for contraction after excitation50-100ms50-100msReaches full contraction afterReaches full contraction after0.5s0.5sDecline in contractile forceDecline in contractile force1-2s1-2sTotal contraction time Total contraction time 1-3s1-3s

SLOWNESS OF ONSET OF SLOWNESS OF ONSET OF CONTRACTION AND RELAXATION OF CONTRACTION AND RELAXATION OF

THE SMOOTH MUSCLE TISSUETHE SMOOTH MUSCLE TISSUE3o times long in comparison of skeletal 3o times long in comparison of skeletal muscle fibersmuscle fibersReasons for tonic and prolonged Reasons for tonic and prolonged contractioncontractionSlow attachment and detachment of cross Slow attachment and detachment of cross bridgesbridgesResponse to calcium ions is much slowerResponse to calcium ions is much slower

FORCE OF MUSCLE FORCE OF MUSCLE CONTRACTIONCONTRACTION

Few myosin filamentsFew myosin filamentsMaximum force of contractionMaximum force of contractionFor skeletal musclesFor skeletal muscles3-4kg/cm2 cross sectional area3-4kg/cm2 cross sectional areaFor smooth musclesFor smooth muscles4-6kg/cm2 cross sectional area4-6kg/cm2 cross sectional areaProlonged period of attachment in Prolonged period of attachment in contractioncontraction

LATCH MECHANISMLATCH MECHANISM

Consumption of less energy for Consumption of less energy for maintenance of contraction as 1/300maintenance of contraction as 1/300

Prolonged tonic contractionProlonged tonic contractionCross bridges phosphorylationCross bridges phosphorylationATP consumption rates fallATP consumption rates fallLittle excitatory signalsLittle excitatory signalsHormonal signalsHormonal signals

STRESS-RELAXATION OF STRESS-RELAXATION OF SMOOTH MUSCLESSMOOTH MUSCLES

Sudden increase in volume of fluid in urinary Sudden increase in volume of fluid in urinary bladderbladder

Stretching the bladderStretching the bladder

Increase in pressureIncrease in pressure

After some time pressure comes to original levelAfter some time pressure comes to original level

STRESS-RELAXATION OF STRESS-RELAXATION OF SMOOTH MUSCLESSMOOTH MUSCLES

Decrease in volumeDecrease in volume

Pressure fallsPressure falls

Comes to original levelComes to original level

Maintenance of pressureMaintenance of pressure

DEFINATION OF STRESS DEFINATION OF STRESS RELAXATION MECHANISMRELAXATION MECHANISM

Ability to return to nearly its original force Ability to return to nearly its original force of contraction sec or min after it has been of contraction sec or min after it has been elongated or shortenedelongated or shortened

Characteristics of unitary type of smooth Characteristics of unitary type of smooth muscles of muscles of visceral type of hollow organsvisceral type of hollow organs

REGULATION OF CONCENTRATION REGULATION OF CONCENTRATION BY CALCIUM IONSBY CALCIUM IONS

Initiation of stimulus for skeletal muscles as Initiation of stimulus for skeletal muscles as well as for smooth muscleswell as for smooth musclesRise in intracellular level of calcium ionsRise in intracellular level of calcium ionsBy means of nerve stimulationBy means of nerve stimulationHormonal signalsHormonal signalsStretching of fibersStretching of fibersSphingosine 1 phosphateSphingosine 1 phosphateChange in chemical environment of fiberChange in chemical environment of fiber

REGULATION OF CONCENTRATION REGULATION OF CONCENTRATION BY CALCIUM IONSBY CALCIUM IONS

Regulatory proteinRegulatory protein

CalmodulinCalmodulin

Similar to troponinSimilar to troponinManner of initation of contraction is Manner of initation of contraction is differentdifferent

SEQUENCE IOF EVENTSSEQUENCE IOF EVENTS

Binding of neurotransmitterBinding of neurotransmitter

Influx of calcium ionsInflux of calcium ions

Binding of calcium ions with calmodulinBinding of calcium ions with calmodulin

Calmodulin-calcium combination joins with Calmodulin-calcium combination joins with myosin kinasemyosin kinase

SEQUENCE IOF EVENTSSEQUENCE IOF EVENTS

Myosin kinaseMyosin kinaseA phosphorylating enzymeA phosphorylating enzymeOne light chain of myosin head is called One light chain of myosin head is called regulatory chainregulatory chainPhosphorylation of myosinPhosphorylation of myosinBinding of actin to myosin due to myosin Binding of actin to myosin due to myosin ATPaseATPaseCross bridges formation occursCross bridges formation occurs

SEQUENCE IOF EVENTSSEQUENCE IOF EVENTS

ContractionContractionDephosphorylation of myosinDephosphorylation of myosinRelaxationRelaxationSustained contraction (latch mechanism)Sustained contraction (latch mechanism)

ROLE OF MYOSIN ROLE OF MYOSIN PHOSPHATASEPHOSPHATASE

Calcium levels falls below critical levelCalcium levels falls below critical levelCessation of contractionCessation of contractionLocated in fluids of smooth musclesLocated in fluids of smooth musclesSplits phosphate from regulatory chainSplits phosphate from regulatory chainCycling stopsCycling stops

POSSIBLE MECHANISM FOR POSSIBLE MECHANISM FOR REGULATION OF THE LATCH REGULATION OF THE LATCH

MECHANISMMECHANISMActivation of myosin kinase and myosin Activation of myosin kinase and myosin phosphatasephosphataseCycling frequency occursCycling frequency occursVelocity of contraction is greatVelocity of contraction is greatActivation of enzyme decreasesActivation of enzyme decreasesLow cycling decreasesLow cycling decreasesDeactivation of both enzymesDeactivation of both enzymesPermit myosin heads to remain attached to actin Permit myosin heads to remain attached to actin filamentfilament

HOW SMOOTH MUSCLES HOW SMOOTH MUSCLES MAINTAIN CONTRATION?MAINTAIN CONTRATION?

Can produce fewer ATPCan produce fewer ATP

SR is much less developedSR is much less developed

Fewer Ca ATPase mole on its membraneFewer Ca ATPase mole on its membrane

IMPORTANCE OF LATCH IMPORTANCE OF LATCH MECHANISMMECHANISM

Less consumption of energyLess consumption of energyLess time requiredLess time required