Expression of calcium channel transcripts in the zebrafish heart: dominance of T-type channels.

Calcium channels are necessary for cardiac excitation-contraction (E-C) coupling, but Ca channel composition of fish hearts is still largely unknown. To this end, we determined transcript expression of Ca channels in the heart of zebrafish (), a popular model species. Altogether, 18 Ca channel α-subunit genes were expressed in both atrium and ventricle. Transcripts for 7 L-type (Ca1.1a, Ca1.1b, Ca1.2, Ca1.3a, Ca1.3b, Ca1.4a, Ca1.4b), 5 T-type (Ca3.1, Ca3.2a, Ca3.2b, Ca3.3a, Ca3.3b) and 6 P/Q-, N- and R-type (Ca2.1a, Ca2.1b, Ca2.2a, Ca2.2b, Ca2.3a, Ca2.3b) Ca channels were expressed. In the ventricle, T-type channels formed 54.9%, L-type channels 41.1% and P/Q-, N- and R-type channels 4.0% of the Ca channel transcripts. In the atrium, the relative expression of T-type and L-type Ca channel transcripts was 64.1% and 33.8%, respectively (others accounted for 2.1%). Thus, at the transcript level, T-type Ca channels are prevalent in zebrafish atrium and ventricle. At the functional level, peak densities of ventricular T-type () and L-type () Ca current were 6.3±0.8 and 7.7±0.8 pA pF, respectively. mediated a sizeable sarcolemmal Ca influx into ventricular myocytes: the increment in total cellular Ca content via was 41.2±7.3 µmol l, which was 31.7% of the combined Ca influx (129 µmol l) via and (88.5±20.5 µmol l). The diversity of expressed Ca channel genes in zebrafish heart is high, but dominated by the members of the T-type subfamily. The large ventricular is likely to play a significant role in E-C coupling.