In the cardiovascular system, T-type calcium channels play an important role for the intracellular calcium homeostasis, spontaneous pacemaker activity and are involved in the progression of structural heart diseases. Androgens influence the cardiovascular physiology and pathophysiology. However, their effect on native I_Ca,T remains unclear. To test the chronic effect of testosterone on the cardiac I_Ca,T cultured neonatal rat ventricular cardiomyocytes were treated with testosterone (1 nM-10 µM) for 24-30 h. Current measurements were performed following testosterone washed-out to exclude any acute testosterone effects. Testosterone (100 nM) pretreatment significantly increased whole-cell I_Ca,T density from 1.26 ± 0.48 pA/pF (n = 8) to 5.06 ± 1.75 pA/pF (n = 7; P < 0.05) and accelerated beating rate. This was attributed to both increased expression levels of the pore-forming subunits Ca_v3.1 and Ca_v3.2 and increased T-type single-channel activity. On single-channel level, the increase of the ensemble average current by testosterone vs. time-matched controls was due to an increased availability (58.1 ± 4.2% vs. 21.5 ± 4.0%, P < 0.01) and open probability (2.78 ± 0.29% vs. 0.85 ± 0.23%, P < 0.01). Cotreatment with the selective testosterone receptor antagonist flutamide (10 µM) prevented these chronic testosterone-induced effects. Conversely, acute application of testosterone (10 µM) decreased T-type single-channel activity in testosterone pretreated cells by reducing the open probability (0.78 ± 0.13% vs. 2.91 ± 0.38%, P < 0.01), the availability (23.6 ± 3.3% vs. 57.6 ± 4.5%, P < 0.01) and the peak current (-20 ± 4 fA vs. -58 ± 4 fA, P < 0.01). Flutamide (10 µM) did not abolish the testosterone-induced acute block of T-type calcium channels.

Our results indicate that long-term testosterone treatment increases while acute testosterone decreases neonatal rat T-type calcium currents. These effects seem to be mediated by a genomic chronic stimulation and a non-genomic acute inhibitory action.