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Acute modulation of Ca2+ influx on rat heart by 17beta-estradiol
C Buitrago1, V Massheimer, A R de Boland
1Departamento de Biologia, Bioquimica & Farmacia, Universidad Nacional del Sur, San Juan, Bahia Blanca, Argentina.
Abstract:
Estrogens initiate their action by binding to specific intracellular receptors and then acting on gene expression. In addition, there is growing evidence of a direct membrane effect via interaction with a cell surphase receptor. The aim of the present study was to investigate the acute effects of 17beta-estradiol on Ca2+ fluxes through second messenger pathways in rat cardiac muscle. Exposure of rat ventricle to low levels of 17beta-estradiol (10(-12)-10(-8) M) increased 45Ca2+ influx within 1 min (+38%); the response was biphasic, peaking at 2 and 5 min (+60 and +55%, respectively). The effect of the hormone on rat heart seems to be specific since 17alpha-estradiol, dihydrotestosterone, and progesterone were devoid of activity. The effect of 17beta-estradiol (5 min, 10(-10) M) was suppressed by nitrendipine (1 microM) and LaCl3 (10 microM), involving the activation of voltage-dependent Ca2+ channels in the acute increase of rat heart calcium influx by the hormone. 17Beta-estradiol rapidly increased cAMP content and PKA activity of rat cardiac muscle in parallel to the changes in Ca2+ uptake. In addition the cAMP antagonist Rp-cAMPS suppressed 17beta-estradiol-dependent Ca2+ influx. Altogether, the data suggest the involvement of the cAMP/PKA messenger system in the nongenomic modulation of Ca2+ influx in rat cardiac muscle by physiological levels of 17beta-estradiol.
Insights
17beta-estradiol rapidly increases calcium influx in rat heart muscle via cell surface receptors. This nongenomic effect involves the cAMP/PKA pathway and voltage-dependent calcium channels.
Area of Science:
- Cardiovascular Physiology
- Endocrinology
- Molecular Cell Biology
Background:
- Estrogens exert genomic effects via intracellular receptors.
- Emerging evidence suggests rapid, nongenomic actions mediated by cell surface receptors.
Purpose of the Study:
- To investigate the acute effects of 17beta-estradiol on calcium (Ca2+) fluxes in rat cardiac muscle.
- To elucidate the second messenger pathways involved in these rapid effects.
Main Methods:
- Exposure of rat ventricular tissue to varying concentrations of 17beta-estradiol.
- Measurement of 45Ca2+ influx.
- Assessment of specificity using related steroids.
- Inhibition studies with nitrendipine, LaCl3, and Rp-cAMPS.
- Measurement of cAMP levels and PKA activity.
Main Results:
- 17beta-estradiol (10(-12)-10(-8) M) significantly increased 45Ca2+ influx within 1 minute, with a biphasic response peaking at 2 and 5 minutes.
- The effect was specific to 17beta-estradiol; 17alpha-estradiol, dihydrotestosterone, and progesterone were inactive.
- Nitrendipine and LaCl3 suppressed the 17beta-estradiol-induced Ca2+ influx, indicating involvement of voltage-dependent Ca2+ channels.
- 17beta-estradiol rapidly elevated cAMP content and PKA activity in parallel with Ca2+ uptake.
- The cAMP antagonist Rp-cAMPS inhibited the 17beta-estradiol-dependent Ca2+ influx.
Conclusions:
- Physiological levels of 17beta-estradiol acutely modulate Ca2+ influx in rat cardiac muscle through a nongenomic mechanism.
- The cAMP/protein kinase A (PKA) signaling pathway is critically involved in this process.
- The rapid effects of 17beta-estradiol on cardiac Ca2+ flux are mediated via cell surface receptors and voltage-dependent Ca2+ channels.