THE EFFECT OF TETRACAINE ON SPONTANEOUS CA2-RETICULUM CALCIUM CONTENTIN RAT VENTRICULAR MYOCYTES( RELEASE AND SARCOPLASMIC)

1. The effects of tetracaine were studied on voltage-clamped rat ventr icular myocytes, which exhibited Ca2+ overload as identified by sponta neous Ca2+ release from the sarcoplasmic reticulum (SR) as shown by th e associated contractions. This Ca2+ release was initially abolished b y tetracaine before returning at a lower frequency: but greater amplit ude, than the control. On removal of tetracaine, there was a burst of spontaneous Ca2+ release activity. All these effects were dose depende nt, from 25 to 200 mu M tetracaine. 2. The spontaneous Ca2+ release ac tivated an inward Na+-Ca2+ exchange current as Ca2+ was pumped out of the cell. The integral of this current (i.e. the Ca2+ efflux) was incr eased in the presence of tetracaine. The calcium efflux per unit time was unaffected by tetracaine. 3. The SR Ca2+ content was increased by tetracaine, as shown by the integral of the caffeine-evoked Na+-Ca2+ e xchange current. The increase of SR Ca2+ content was equal to the extr a Ca2+ lost from the cell during the burst on removal of tetracaine, a nd to estimates of the extra calcium gained over the quiescent period following addition of tetracaine. 4. It is concluded that partial inhi bition of calcium-induced calcium release increases SR Ca2+ content. I n the steady state, cell Ca2+ balance is maintained as the lower frequ ency of spontaneous release (that activates efflux) is compensated for by their greater size.