249 research outputs found
Effects of norepinephine, calcium, and rate of discharge on 42K movements in canine cardiac Purkinje fibers.
No full text
Electrical coupling affects the repolarization phase of action potential and its beat to beat variability in pairs of guinea pig ventricular myocytes
No full text
Spontaneous electrical uncoupling in double-current clamped cardiac myocyte pairs
No full textWhole-cell Double-Voltage Clamp is usually employed rather than Double-Current Clamp (DCC) for measuring intercellular electrical resistance (Rj), which is known to rise spontaneously after double-cell attachment in cardiac myocyte pairs. We tested reliability of DCC estimates of Rj in pairs of rat and guinea pig (gp) ventricular myocytes, artificially coupled with a variable external resistance, showing an accuracy >95% for a coupling range of 4<Rj<80 Mohm. Using a mathematical model and experimental results, we showed that, underestimate of Rj for coupling values above this range, is due to membrane resistance non-linearity for hyperpolarized potentials (Vm) close to resting potential (Vr) (Vr-Vm<3 mV) and can be minimized when such non-linearity is measured in single cells and taken into account in the calculation of Rj. A DCC protocol was therefore applied which allowed, at a frequency of 1Hz, to simultaneously sample Rj and sequentially pace real ventricular myocyte pairs. Within the first 7 min after double-patching, paced gp pairs showed faster spontaneous uncoupling than paced rat pairs ( 11.8 +/- 2.1 Mohm/min, n=6 vs 2.0 +/- 0.8 Mohm/min, n=6) and lower initial Rj (18.0 +/- 3.1 Mohm, n=27 vs 32.6 +/- 4.9 Mohm, n=28). Also, not-pacing or buffering intracellular calcium ([Ca2+]i) with 14 mM BAPTA or 14 mM EGTA, decreased the rate of spontaneous uncoupling in gp pairs (0.9 +/- 0.8 Mohm/min, n=4; 0.3 +/- 0.2 Mohm/min, n=4; 2.7 +/- 1.1 Mohm/min, n=3 respectively). We conclude that DCC approach gives accurate estimates of Rj, which spontaneously increases following cell attachment at different rate in gp and rat myocyte pairs, being the rate of uncoupling pacing- and [Ca2+]i-dependent
- …
