Cav1.3 channels produce persistent calcium sparklets, but Cav1.2 channels are responsible for sparklets in mouse arterial smooth muscle

Ca2(+) sparklets are local elevations in intracellular Ca2(+) produced by the opening of a single or a cluster of L-type Ca2(+) channels. In arterial myocytes, Ca2(+) sparklets regulate local and global intracellular Ca2(+). At present, the molecular identity of the L-type Ca2(+) channels underlying Ca2(+) sparklets in these cells is undetermined. Here, we tested the hypotheses that voltage-gated calcium channel-alpha 1.3 subunit (Ca(v)1.3) can produce Ca2(+) sparklets and that Ca(v)1.2 and/or Ca(v)1.3 channels are responsible for Ca2(+) sparklets in mouse arterial myocytes. First, we investigated the functional properties of single Ca(v)1.3 channels in tsA201 cells. With 110 mM Ba2(+) as the charge carrier, Ca(v)1.3 channels had a conductance of 20 pS. This value is similar to that of Ca(v)1.2 and native L-type Ca2(+) channels. As previously shown for Ca(v)1.2 channels, Cav1.3 channels can operate in two gating modes characterized by short and long open times. Expressed Ca(v)1.3 channels also produced Ca2(+) sparklets. Ca(v)1.3 sparklets had properties similar to those produced by Ca(v)1.2 and native L-type channels, including quantal amplitude, dihydropyridine sensitivity, bimodal gating, and dual-event duration times. However, the voltage dependencies of conductance and steady-state inactivation of the Ca2(+) current (ICa) in arterial myocytes were similar to those recorded from cells expressing Ca(v)1.2 but not Ca(v)1.3 channels. Furthermore, nifedipine (10 mu M) eliminated Ca2(+) sparklets in wild-type myocytes but not in myocytes expressing dihydropyridine-insensitive Ca(v)1.2 channels. Accordingly, Ca(v)1.3 transcript and protein were not detected in isolated arterial myocytes. We conclude that although Ca(v)1.3 channels can produce Ca2(+) sparklets, Ca(v)1.2 channels underlie ICa, Ca2(+) sparklets, and hence dihydropyridine-sensitive Ca2(+) influx in mouse arterial myocytes.