L-type and T-type Ca2+ current in cultured ventricular guinea pig myocytes

The aim of this investigation was to study L-type and T-type Ca 2 + current (I C a L and I C a T ) in short-term cultured adult guinea pig ventricular myocytes. The isolated myocytes were suspended in serum-supplemented medium up to 5 days. Using whole-cell patch clamp techniques I C a L and I C a T were studied by applying voltage protocols from different holding potentials (-40 and -90 mV). After 5 days in culture the myocytes still showed their typical rod shaped morphology but a decline in cell membrane capacitance (26 %). The peak density of I C a T was reduced significantly between day 0 (-1.6′0.37 pA/pF, n=9) and day 5 (-0.4′0.13 pA/pF, n=11), whereas peak I C a L density revealed no significant differences during culturing. The I C a T /I C a L ratio dropped from 0.13 at day 0 to 0.05 at day 5. Compared with day 0 I C a L the steady state inactivation curve of day 1, day 3 and day 5 myocytes was slightly shifted to more negative potentials. Our data indicate that guinea pig ventricular L-type and T-type Ca 2 + channels are differently regulated in culture.