CHANGE IN THE CONTRACTILITY OF RAT ATRIAL MUSCLE BY COLD PRESERVATION

Abstract

Cold preservation of isolated mammalian hearts attenuates cardiac contractility. We examined the effect of intracellular and extracellular Ca ion on the contractility of cold-preserved atria of rat. Rat hearts were isolated and stored in Collins' solution at 4°C for either 0 or 12 h. Mechanical responses were then examined in electrically driven left and beating right atrial muscle preparations. When stimulus frequencies were increased stepwise from 0.1 to 3 Hz, the twitch contractions initially decreased (Woodworth phenomenon: WP) and then increased (Bowditch phenomenon: BP) in 0 hour-preserved (fresh) left atrial preparations. However, BP, but not WP, was abolished in 12 hour-preserved preparations. The absence of BP was also observed when fresh preparations were exposed to a low-Ca medium (0.9 mM) . Ryanodine (3×10^-8 M) abolished the twitch contractions at low stimulus frequencies, but did not inhibit BP in fresh preparations. In 12 hour-preserved preparations, both ryanodine and low-Ca medium completely inhibited the twitch contraction. The positive inotropic effects of isoproterenol in right and left atria were markedly attenuated after 12-hour cold preservation. However, the rate of spontaneous beating and the positive chronotropic effect of isoproterenol in right atria were not changed in the cold-preserved preparations or in fresh preparations that had been treated with ryanodine or exposed to a low-Ca medium. These results clearly show that cold-preserved atrial muscle is more susceptible to changes in intracellular and extracellular Ca ion and suggest that the attenuation of cardiac contractility by cold preservation may be due to the impairment of Ca²⁺ influx which may result from membrane deterioration.