In the cardiovascular system,
T-type calcium channels play an important role for the intracellular
calcium homeostasis and 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 T-type
calcium currents (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 microM) for 24-30 h. Current measurements were performed after
testosterone washout 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(v)3.1 and Ca(v)3.2 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 mum) prevented these chronic
testosterone-induced effects. Conversely, acute application of
testosterone (10 microM) 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), availability (23.6 +/- 3.3 vs. 57.6 +/- 4.5%, P < 0.01), and peak current (-20 +/- 4 vs. -58 +/- 4 fA, P < 0.01).
Flutamide (10 microM) did not abolish the
testosterone-induced acute block of
T-type calcium channels. Our results indicate that long-term
testosterone treatment increases, whereas acute
testosterone decreases neonatal rat T-type
calcium currents. These effects seem to be mediated by a genomic chronic stimulation and a nongenomic acute inhibitory action.