<prompt> Long acting calcium channel act in which pa of action potential?0123  <response>: Phases Characteristics 0 depolarization Opening of fast Na channels. 1 initial repolarization Closure of fast Na channels K efflux through open K channels. 2 plateau L - type slow Ca channels open fast K channels close. 3 rapid repolarization Ca channels close slow K channel open. 4 resting membrane potential Average around - 90 mv. 