Electrical properties of individual cells isolated from adult rat ventricular myocardium.

Abstract

1. Individual cells were isolated from adult rats ventricular myocardium by a collagenase digestion procedure. 2. Steady membrane potentials recorded with conventional intracellular glass micro-electrodes from cells in a modified Krebs solution containing 3 . 8 mM-KCl and 0 . 5 mM-CaCl2 were less negative than -40 mV in most cells (-25 . 3 +/- 10 . 9 mV, mean +/- S.D., 211 cells). 3. After addition of the potassium selective ionophore valinomycin (60 nM) to the bathing solution all recorded membrane potentials were more negative than -60 mV (-74 . 8 +/- 7 . 0 mV, sixty-three cells). 4. The internal concentration of potassium in the cells was determined as 120 . 8 +/- 1 . 7 mM (+/- S.E., n = 24) by flame emission spectrometry after centrifugation through silicone oil, using tritiated water and D-[1-14C] mannitol to estimate total and extracellular water in the pellet. 5. In the majority of cells in the standard solution the membrane potential recorded within a few msec of penetration was more negative than -70 mV (-78 . 4 +/- 9 . 7 mV, seventy-three cells). In sixty-six cells penetration initiated an action potential which overshot zero by 31 . 3 +/- 7 . 1 mV. This overshoot was abolished by reducing the external sodium to 0 . 1 of the normal value, and reduced or abolished by addition of tetrodotoxin (30 microM). 6. Modifications of the standard bathing solution which increased the number of cells with steady recorded membrane potentials more negative than -60 mV were: isosmotic substitution of sucrose for NaCl; replacement of NaCl and KCl by sodium isethionate and potassium methyl sulphate; addition of 5 or 10 mM-CaCl2; addition of 10 mM-MnCl2. 7. For cells in solution containing 2 . 5 or 5 . 5 mM-CaCl2, input resistances estimated from the amplitude of hyperpolarizations evoked by 200 msec current pulses were approximately 40 M omega at a resting potential close to -80 mV and became much greater as cells were depolarized. Time constants measured at the resting potential were approximately 8 msec. 8. In certain conditions, repeated spontaneous action potentials were recorded from contracting cells, and in quiescent cells evoked action potentials could be initiated by applying brief depolarizing pulses through the micro-electrode. Action potentials were coincident with contractions. 9. It is concluded that the resting potential of these isolated cells is normally more negative than -70 mV, and that the cells retain the ionic mechanisms necessary for the generation of active currents.

The effects of caffeine on the electrical properties of isolated, single rat ventricular cells.

“…These results are comparable to those obtained with caffeine. Similar increases in the plateau and duration of the action potential have been observed in other studies with isolated myocytes (POWELL et al, 1978;TANIGUCHI et al, 1981;ISENBERG and KLOCKNER, 1982a).…”

“…Accumulation of cyclic AMP in response to catecholamine has already been observed in isolated rat myocardium (MousTAFA et al, 1976;PoWELL et al, 1978). Thus, our finding that the effect of caffeine in the membrane currents is similar to that of adrenaline suggests that the effects of caffeine and catecholamine are both mediated by increases in cyclic AMP.…”

“…Adrenaline increased the amplitude and duration of the action potential in isolated myocytes. In voltage-clamp experiments, adrenaline was found to increase IS substantially without changing the shape of the I V curve (PoWELL et al, 1978;TANIGUCHI et al, 1981;ISENBERG and KLOCKNER, 1982b). We found that adrenaline produced almost no changes in the outward current.…”

Enhancement of delayed rectifier K+ current by P2‐purinoceptor stimulation in guinea‐pig atrial cells.

“…Cell preparation Atrial cells were obtained from guinea-pig hearts by an enzymatic dissociation procedure similar to that previously described (Powell, Terrar & Twist, 1980). Briefly, guinea-pigs (250-400 g body weight) were killed by an overdose of sodium pentobarbitone (120 mg kg-' i.P.)…”

Induction and potential biological relevance of a Ca2+‐independent nitric oxide synthase in the myocardium

“…Cardiac myocytes from adult rats (250-350 g) were isolated by perfusion of the isolated heart with collagenase as described (Powell et al, 1980;Stone et al, 1989). The final cell preparation containing approximately 55% viable (i.e.…”