Key Points
- To characterize the phases and voltage dependence of tension fall following depolarization-induced contraction in bullfrog atrial muscle.
- Applied the double glycerol-gap voltage clamp technique to bullfrog atrial muscle preparations at 17°C.
- Evaluated mechanical tension decline across depolarization steps ranging from 25 to 80 mV, tracking time constants across different membrane potentials.
- Tension fall resolved into three phases: initial retardation (time constant 0.07–0.08 s), principal rapid relaxation (time constant 0.3–0.4 s), and final slow relaxation.
- The time constant of the principal relaxation phase increased hyperbolically with depolarization, exhibiting a direct dependence on membrane potential levels before and after repolarization.
- The logarithm of late tension approximately 1 second after repolarization scaled linearly with membrane potential on the depolarizing side, but became voltage-independent during hyperpolarization.
Structured PICO
PPopulationBullfrog atrial muscle
IInterventionVoltage clamp by the double glycerol-gap technique
OOutcomeTension fall after termination of a depolarizationsurrogate
This preclinical study characterizes the three phases of tension fall in bullfrog atrial muscle following depolarization, suggesting roles for Ca influx and Na-Ca exchange.