Summary
5-Hydroxytryptamine (10 μmol/l; 5-HT) exerted a positive inotropic effect associated with an increase in the Ca2+ current (ICa) in the human right atrium. For detailed analysis, L-type Ca2+ channel currents were recorded from cell-attached patches using 100 mmol/l Ba2+ as charge carrier. Ca2+ channel activity was identified, first, by burstlike inwardly directed currents and, second, by the appearance of long channel openings promoted by Bay K 8644 (1 μmol/l) upon repetitive depolarizations from − 80 to 0 mV The unitary conductance of the Ca2+ channel amounted to 25.8 pS. During superfusion with 5-HT, ensemble averaged (mean) current was enhanced by about 60%. The increase in mean current was brought about by an increase in the channel availability, defined as the ratio of sweeps containing Ca2+ channel activity to the total number of depolarizations. The open probability of a single Ca2+ channel within a sweep with channel activity, unitary conductance, mean open and mean shut times of the channel, however, remained unaffected during superfusion with 5-HT (n = 10). The 5-HT-induced increase in macroscopic ICa in the human atrium can therefore be explained by an enhanced availability of Ca2+ channels to open upon depolarization. The observed changes in gating properties of the human Ca2+ channel by 5-HT are very similar to those which are known from isoprenaline-induced CAMP-dependent phosphorylation of the Ca2+ channel protein in other tissues.
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Jahnel, U., Nawrath, H., Rupp, J. et al. L-type calcium channel activity in human atrial myocytes as influenced by 5-HT. Naunyn-Schmiedeberg's Arch Pharmacol 348, 396–402 (1993). https://doi.org/10.1007/BF00171339
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DOI: https://doi.org/10.1007/BF00171339