L- and T-Type Calcium Channels in Acutely Isolated Neonatal and Adult Cardiac Myocytes

Abstract

ABSTRACT: We have compared transsarcolemmal Ca²⁺ currents in acutely isolated neonatal (1− to 5-d-old) and adult rabbit cardiac myocytes prepared using similar enzymatic techniques. Time- and voltage-dependent inward Ca²⁺ currents were measured using the whole-cell voltage clamp technique. In neonatal myocytes, peak Ca²⁺ currents measured 114 ± 10 pA (mean ± SEM, n = 18) as compared with 2014 ± 403 pA in adult myocytes (n = 5, p < 0.001). Although adult myocytes had a larger surface area (estimated from cell capacitance) than neonatal cells (113 ± 15 × 10^-6 versus 28 ± 2 × 10^-6 cm², p < 0.001), the calculated peak current density was also significantly larger in adult cells (17.9 ± 2.5 compared to 4.3 ± 0.4 μA/cm² for neonatal cells, p < 0.001). The voltage dependence of the peak Ca²⁺ current was similar in neonatal and adult myocytes. Early transient (T-type) Ca²⁺ currents were also studied by comparing the current induced by depolarization to —20 mV from holding potentials of −40 and −80 mV. T-type Ca²⁺ channels were present in 91% of the adult cells but were evident in only 39% of the neonatal cells. In summary, voltage-gated Ca²⁺ current amplitude, current density, and T-type Ca²⁺ channel prevalence all increase with maturation. These data suggest that neonatal myocytes may be relatively deficient in Ca²⁺ channel activity when compared to adult myocytes.

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