Question

During the smooth muscle lab, we added KCl to the water bath effectively increasing the extracellular K+ concentration. Describe on a molecular level, how the addition of KCl to the water bath led to increased contraction of the gut tissue.

Answer 1

The excitability of a muscle depends upon its resting membrane potential. Normally smooth muscle has resting membrane potential of -55 to -40 mV. For genetation of action potential membrane potential has to be increased upto threshold potential. Threshold potential for smooth muscle is around -40 mV. Hence smooth muscle does not have steady Resting memberane potential. Rather, they have spike potential.

Resting membrane potential depends on ,

Difusion of K+: This is the most important cause. The most permeable ion in resting condition of cell
is K+ >>Cl- >>Na+.

When gut is bathed in KCl solution -

Excess ECF K+ decreases the difusion of K+ from cell. This cause extra K+ (positive charge) inside cell. this brings RMP closer to threshold potential hence muscle depolarise.

Hence KCl to the water bath led to increased contraction of the gut tissue.