A, activation of the L-type Ca2+ current (200 ms) elicited a substantial Ca2+ release signal. Both the current and the Ca2+ signal were markedly enhanced by administration of 1 μm isoproterenol in the bathing solution. B, in an analogous experiment, activation of the Na+ current (50 ms) in a different cell showed smaller Ca2+ signal amplitudes but similar β-adrenergic potentiation. Traces show from top to bottom: voltage protocol (mV), current record, line-scan image, mean Ca2+ concentration profile, same current record expanded 10 times (red traces, not temporally aligned to the other signals).