The effect of adrenomedullin on the L-type calcium current in myocytes from septic shock rats: Signaling pathway

Abstract

Adrenomedullin (ADM) is upregulated in cardiac tissue under various pathophysiological conditions, particularly in septic shock. The intracellular mechanisms involved in the effect of ADM on adult rat ventricular myocytes are still to be elucidated. Ventricular myocytes were isolated from adult rats 4 h after an intraperitoneal injection of lipopolysaccharide (LPS, 10 mg/kg). Membrane potential and L-type calcium current (ICa,L) were determined using whole cell patch-clamp methods. APD in LPS group was significantly shorter than control values (time to 50% repolarization: LPS, 169 ± 2 ms; control, 257 ± 2 ms, P < 0.05; time to 90% repolarization: LPS, 220 ± 2 ms; control, 305 ± 2 ms, P < 0.05). ICa,L density was significantly reduced in myocytes from the LPS group (-3.2 ± 0.8 pA/pF) compared with that of control myocytes (-6.7 ± 0.3 pA/pF, P < 0.05). The ADM antagonist ADM-(22-52) reversed the shortened APD and abolished the reduction of ICa,L in shock myocytes. In myocytes from control rats, incubating with ADM for 1 h induced a marked decrease in peak ICa,L density. This effect was reversed by ADM-(22-52). The G i protein inhibitor, pertussis toxin (PTX), the protein kinase A (PKA) inhibitor, KT-5720, and the specific cyclooxygenase 2 (COX-2) inhibitor, nimesulide, reversed the LPS-induced reduction in peak ICa,L. The results suggest a COX-2-involved PKA-dependent switch from Gs coupled to PTX-sensitive Gi coupling by ADM in adult rat ventricular myocytes. The present study delineates the intracellular pathways involved in ADM-mediated effects on ICa,L in adult rat ventricular myocytes and also suggests a role of ADM in sepsis. Copyright © 2007 the American Physiological Society.