Sodium channel inactivation from resting states in guinea-pig ventricular myocytes.
AUTOR(ES)
Lawrence, J H
RESUMO
1. Unitary Na+ channel currents were recorded from isolated guinea-pig ventricular myocytes using the cell-attached patch-clamp technique with high [Na+] in the pipette to enhance the signal-to-noise ratio. 2. The probability that the channel enters the inactivated state (I) directly from resting states (C) was investigated over a wide range of membrane potentials. 3. At membrane potentials of -60 mV or more positive, Markov chain theory was used to estimate the probability of C----I from histograms of the number of channel openings per depolarizing period. Holding potentials at least as negative as -136 were required to ensure that all channels resided in C prior to depolarization. 4. At membrane potentials negative to -60 mV, a two-pulse protocol was employed to determine the probability of C----I from the fraction of blank sweeps during the pre-pulse with correction for missed events. 5. The probability of C----I was found to be steeply voltage dependent at negative potentials, falling from 0.87 +/- 0.03 (mean +/- S.D.) at -91 mV to 0.42 +/- 0.01 at -76 mV. At potentials positive to -60 mV, this probability was less steeply voltage dependent and decayed to near zero at 0 mV. 6. Under physiological conditions, C----I transitions may produce appreciable Na+ channel inactivation at diastolic potentials. At potentials above the action potential threshold, inactivation is much more likely to occur from the open state.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1179863Documentos Relacionados
- Sodium current-induced calcium signals in isolated guinea-pig ventricular myocytes.
- Inactivation of outward Na(+)-Ca2+ exchange current in guinea-pig ventricular myocytes.
- Sodium-dependent membrane current induced by carbachol in single guinea-pig ventricular myocytes.
- Extracellular osmotic pressure modulates sodium-calcium exchange in isolated guinea-pig ventricular myocytes.
- Microheterogeneity of subsarcolemmal sodium gradients. Electron probe microanalysis in guinea-pig ventricular myocytes.