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Excitation-contraction
coupling in smooth muscle is believed to occur by two
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mechanisms-electromechanical
and pharmacomechanical coupling.
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Electromechanical
coupling operates through changes in surface membrane potential;
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typically resting
membrane potential= -40 to -70 mV.
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Primary drive
for the rise in intracellular calcium is membrane depolarization, with the
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consequential
opening of voltage operated calcium channels; neurotransmitters or
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hormones acting
to depolarize the membrane will cause contraction while those
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producing
membrane hyperpolarization will cause relaxation.
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Like
cardiac muscle, the influx of Ca2+ likely causes release of Ca2+
from sarcoplasmic
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reticulum.
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