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Indian Journal of Biochemistry and Biophysics (IJBB) >
IJBB Vol.42 [2005] >
IJBB Vol.42(2) [April 2005] >
| Title: | Modulation of spontaneous electrical activity of freshly isolated 3-day embryonic chick ventricle by cAMP and cGMP |
| Authors: | Prakash, P
Tripathi, O |
| Keywords: | cAMP
cGMP
Action potential
Embryonic chick ventricle
Spontaneous electrical activity
Ca²⁺ channel
Chronotropic effect |
| Issue Date: | Apr-2005 |
| Publisher: | CSIR |
| IPC Code: | C07H19/00, 19/20 |
| Abstract: | Effects of cyclic nucleotides 8-Bromo-cAMP and 8-Bromo-cGMP (membrane permeable analogs of cAMP and cGMP) were examined on action potential (AP) configuration and rate of spontaneous firing of the freshly isolated 3-day embryonic chick ventricle (ECV) to assess the role of L-type slow Ca²⁺ channels in upstroke of AP and spontaneous electrical activity (pacemaker potential). The 3-day ECV exhibited prominent automaticity and spontaneous APs characterized by maximum upstroke velocity (+Vmax), maximum diastolic potential (MDP), overshoot (Eov), AP duration at -20 mV (APD₂₀) and cycle length (CL) of 33.09±3.18 V/sec, -63.77±1.17 mV, 17.40±0.91 mV, 51.20±3.05 m sec and 795±150 m sec, respectively (n= 10 preparations). 8-Br-cAMP (1 mM) caused significant increase in Eov and APD₂₀ (37% and 56%, respectively, p<0.01), but failed to produce any stimulatory effect on +Vmax and MDP. Surprisingly, 8-Br-cAMP produced negative chronotropic effect on spontaneous firing (automaticity) and enhanced the CL significantly by 43% (p<0.05). 8-Br-cGMP, however, had no effect on AP configuration and the rate of spontaneous firing. The present findings with 8-Br-cAMP suggest that L-type slow Ca²⁺ channels do not contribute to upstroke of AP and pacemaker potential of spontaneously firing freshly isolated 3-day ECV. The negative chronotropic effect of 8-Br-cAMP suggests that the ionic mechanism underlying pacemaker potential is [Ca]i-dependent. However, the lack of any effect of 8-Br-cGMP on spontaneous electrical activity of freshly isolated 3-day ECV indicates that cGMP does not modulate the basal Ca²⁺ channel activity in young embryonic myocardium. |
| Page(s): | 118-121 |
| ISSN: | 0301-1208 |
| Source: | IJBB Vol.42(2) [April 2005]
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