Effects of Norepinephrine and Epinephrine on Resting Membrane Potential in Body Wall Muscle Cells of Lumbricus Terrestris Eearthworm

Norepinephrine and to a lesser extent epinephrine increased the resting membrane potential of earthworm body wall muscle cells. Ouabain, phentolamine, propranolol, and replacement of Ca(2+) with Mg(2+) in the incubation medium abolished this effect. External 3'5'-cAMP in high concentration, dibutyryl cAMP, and dibutyryl cGMP did not induced hyperpolarization of muscle cell membranes. It was concluded that norepinephrine and epinephrine increased the resting membrane potential in earthworm body wall muscle cells via activation of Na(+), K(+) pump. This process involves Ca(2+) and sarcolemmal adrenergic structures, similar to alpha-adrenoceptors in vertebrate, but not the cyclic nucleotide systems.