Premium
Characteristics of nitric oxide‐mediated cholinergic modulation of calcium current in rabbit sino‐atrial node
Author(s) -
Han X.,
Kobzik L.,
Severson D.,
Shimoni Y.
Publication year - 1998
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1998.741bm.x
Subject(s) - nitric oxide , rabbit (cipher) , cholinergic , acetylcholine , chemistry , nitric oxide synthase , calcium , medicine , endocrinology , pharmacology , neuroscience , biophysics , biology , computer science , computer security
1 We have previously shown that nitric oxide (NO) production is essential for cholinergic inhibition of the β‐adrenergic stimulated L‐type calcium current ( I Ca‐L ) in rabbit pacemaker (sino‐atrial node (SAN)) cells. The present experiments demonstrate the presence of constitutive nitric oxide synthase (cNOS) in SAN cells, and characterize the NO‐mediated cholinergic response. 2 Immunohistochemical staining, using an antibody prepared against endothelial cNOS, demonstrated that this enzyme was present in single myocytes obtained from the SAN. 3 The activation of cNOS is known to be Ca 2+ and calmodulin dependent. Strongly buffering intracellular Ca 2+ with the membrane‐permeable chelator BAPTA‐AM (10 μM) significantly reduced (and in some cases abolished) the attenuation of I Ca‐L by the muscarinic agonist carbamylcholine (CCh). In contrast, the CCh‐induced activation of an outward K + current, I K,ACh , was unaffected by buffering of [Ca 2+ ] i . The calmodulin inhibitor 48/80 (20 μM) also abolished the attenuation of I Ca‐L by CCh, with no change in the activation of I K,ACh . 4 Neither thapsigargin nor ryanodine (5‐10 μM), agents which deplete intracellular Ca 2+ stores, significantly changed the attenuation of I Ca‐L by CCh. 5 Pertussis toxin (PTX) completely abolished both the inhibitory action of CCh on I Ca‐L and the activation of I K,ACh . This establishes that a PTX‐sensitive GTP‐binding protein links the muscarinic receptor to NO synthase activation in SAN cells. 6 Our hypothesis is that NO leads to activation of a cyclic GMP (cGMP)‐activated phosphodiesterase (PDE II) as a mechanism for enhanced cyclic AMP breakdown and I Ca‐L attenuation. This was supported by showing that a specific inhibitor of PDE II, erythro‐9‐(2‐hydroxy‐3‐nonyl) adenine (EHNA), blocks the effect of CCh on I Ca‐L , but not on I K,ACh . Using reverse transcriptase‐polymerase chain reaction techniques, we have established that PDE II is the dominant cyclic nucleotide phosphodiesterase isoform in SAN cells.