IONIC DEPENDENCE OF THE RESPONSE TO ACETYLCHOLINE OF A MOLLUSCAN BUCCAL MUSCLE - RADULAR PROTRACTOR OF BUSYCON-CANALICULATUM

1. We studied the ionic dependence of the response of a molluscan phasic smooth muscle to applied acetycholine (ACh). 2. In sodium-free medium, ACh depolarization was eventually greatly reduced and contracture-force was nearly abolished. 3. Potassium-free medium did not affect ACh depolarization or contracture-force. 4. Exposure to low-calcium medium did not lead to a reduction in amplitude of ACh depolarization but force in low-calcium medium was eventually reduced to zero. 5. These results are consistent with involvement of inward Na+ current in depolarization by ACh and of Ca2+ in excitation-contraction coupling. © 1979.