Blocking L-calcium current by l-tetrahydropalmatine in single ventricular myocyte of guinea pigs

AIM: To study the effect of l-tetrahydropalmatine (l-THP) on L-type calcium channel. METHODS: Patch clamp technique (whole cell recording) was used to record L-Ca2+ current in single cardiac myocyte. RESULTS: 1) l-THP 1, 10, and 100 mu mol.L-1 reduced ICa-max from (999 +/- 93) pA to (700 +/- 111) pA , (582 +/- 66) pA, and (420 +/- 112) pA (n = 6, P < 0.01), respectively. 2) l-THP reduced the voltage at half-maximal inactivation (V-1/2) of L-Ca2+ c hannel to more negative potentials by 9 mV (n = 5, P < 0.05). 3) l-THP caus ed both tonic and use-dependent reduction of Ca2+ current. Tonic block of l -THP on Ca2+ current was 46 % +/- 8 % (n = 6, P < 0.01). The degree of use dependent blocking was 13.5 % +/- 2.4 % (n = 6, P < 0.05) at 1 Hz, the degr ee increased to 44 % +/- 5 % (n = 6, P < 0.01) at 3 Hz. 4) l-THP delayed ha lf-recovery time of Ca2+ channel recovery from inactivity from (94 +/- 39) ms to (170 +/- 4 2) ms ( n = 6, P < 0.01). CONCLUSION: l-THP has a moderate inhibitory effect on L-Ca2+ current.