C 044: NOVEL MODEL FOR “CALCIUM PARADOX” IN SYMPATHETIC TRANSMISSION OF SMOOTH MUSCLES

J Pharm Pharmacogn Res 2(Suppl. 1): S121, 2014

Special supplement with the abstract book of LATINFARMA 2013

Conference

C 044: NOVEL MODEL FOR “CALCIUM PARADOX” IN SYMPATHETIC TRANSMISSION OF SMOOTH MUSCLES: ROLE OF CYCLIC AMP PATHWAY

Bergantin LB, Souza CF, Miranda-Ferreira R, Smaili SS, Jurkiewicz NH, Jurkiewicz A, Caricati-Neto A.

Department of Pharmacology – INFAR. Escola Paulista de Medicina, Federal University of São Paulo, Brazil.
Abstract

Previous studies showed that activity contractile of smooth muscles in response to transmitters released from sympathetic nerves is dramatically reduced by inhibition of Ca2+ influx through L-type voltage-dependent Ca2+ channel (L-type VDCC) or increase of cytosolic cAMP concentration ([cAMP]c) (Burnstock, Ann Rev Pharmacol Toxicol 2009). In recent study (Cell Calcium 2013, submitted), we showed that simultaneous administration of L-type VDCC blockers (verapamil) and [cAMP]c enhancers (rolipram, IBMX and forskolin) potentiated purinergic contractions evoked by electrical field stimulation of rat vas deferens, instead of strongly inhibiting. However, molecular mechanisms involved in this “calcium paradox” are yet unclear. In the present work, we showed that this potentiation of purinergic contraction of rat vas deferens was prevented by inhibitors of adenylyl cyclase (SQ 22536) and blockers of Ca2+ uptake by sarco-endoplasmic reticulum (thapsigargin), suggesting that this effect is mediated by increment of cytosolic Ca2+ concentration ([Ca2+]c) mediated by cAMP. To evaluate if combination of inhibition of Ca2+ influx and increase of [cAMP]c produces increment of [Ca2+], we studied effects of verapamil and rolipram on fura-2 signals (Ca2+ probe) in chromaffin cells of rat adrenal medulla using fluorescence microscopy. These assays showed that [Ca2+]c in these cells was increased by combination of these agents. This effect was prevented by preincubation with thapsigargin, suggesting participation of Ca2+ from sarco-endoplasmic reticulum. In contrast, a reduction of [Ca2+]c was observed when verapamil and rolipram were incubated alone. Together, these results suggest that reduction of [Ca2+]c due to blockade of Ca2+ influx through L-type VDCC could stimulate adenylyl cyclase activity increasing [cAMP]c that in response stimulates Ca2+ release from endoplasmic reticulum, resulting in an increment of transmitter release from sympathetic nerves and contraction. This interaction between Ca2+ and cAMP signaling pathway could be important in the regulation of neurotransmission and in adverse effects of combined use of anti-hypertensive and antidepressants.