Temperature Effects on Pharmacologic Enhancement of L-Type Calcium Current

L-type calcium current (Cav1.2) plays a key role in modulation of multiple cardiovascular functions. Therefore, Cav1.2 calcium current assay is useful in screening discovery compounds for potential cardiovascular (CV) liabilities. L-type calcium current itself is highly sensitive to temperature. However, it is not known if drug effects on this current are influenced by temperature. Using whole-cell voltage clamp techniques, we compared the effects of room (22-24° C) and physiological (37° C) temperatures on the current in the absence and presence of a calcium current activator (TTYC) in CHO cells stably expressing L-type calcium channels. Under our experiment conditions (2 mM [Ca2+]o), calcium current amplitude in CHO cells was increased approximately 4-fold with warming from 24 to 37° C; the half maximal activation voltage (V1/2) was shifted from −6.4 mV (24° C) to −17 mV (37° C). The calcium channel activator TTYC (0.3 uM, Su et al. 2010) increased peak current by 92 ± 10 % at 24° C but only 20 ± 3.0% at 37° C; time to peak increased from 2.4 ± 0.4 to 34.5 ± 2.4 ms (control vs TTYC) at room temperature and from 5.6 ± 0.4 to 130 ± 14 ms at 37° C. TTYC produced similar V1/2 shifting (to the left) in the activation curves at room (−10.2 vs. −2.2 mV) and physiology (−23.5 vs. −14.2 mV) temperatures. In summary, these results confirm that temperature is an important modulator of the L-type calcium channels expressed in CHO cells, and further demonstrate that the natural modulator (temperature) of L-type calcium channel influences its pharmacological responses to a channel activator in terms of peak current amplitude and biophysical properties.