Rhythmic coronary arterial contractions: changes with time and membrane potential.

Responses of isolated rabbit coronary artery segments to KCl and 2-(2-aminoethyl)-pyridine (AEP) were studied. Vessels stored at 2 degrees C for 24 h developed spontaneous rhythmic contractions during the first 20 min in Krebs solution at 37 degrees C. The contractile response to KCl or AEP declined to a minimum at 60 min [i.e., time zero (to) +60], increased to a peak at to +150 and then again declined. Resting membrane potential (Em) was less than or equal to -40 mV at to +20, -70 mV at to +30-60 and -50 mV at to +240-360 min. Rhythmic contractile responses were frequent and were associated with changes in Em. Vessels that were not cold stored did not hyperpolarize, nor did they show the early decline in response. Vessels stored at 2 degrees C for 24 h and then tested at 22-23 degrees C exhibited a similar pattern of changes in contraction but the time course was more protracted. We conclude that contractile responses are initially modulated by changes in Em associated with an increase then decrease in the activity of the sodium pump. Later changes in reactivity are due to a different mechanism.