| Autor: |
Shrier, Alvin, Clay, John, Shrier, A, Clay, J R |
| Předmět: |
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| Zdroj: |
Journal of Membrane Biology; 1982, Vol. 69 Issue 1, p49-56, 8p |
| Abstrakt: |
We have investigated the pacemaker properties of aggregates of cells dissociated from the atria and ventricles of 10 to 14-day-old chick embryonic hearts using a two-microelectrode current and voltage-clamp technique. These preparations usually beat spontaneously and rhythmically in tissue culture medium containing 1.3m m potassium with a beat rate typically in the range of 15-60 beats per minute. The beat rate results show considerable variability, which precludes any statistically significant comparison between the spontaneous activity of atrial and ventricular cell preparations at 10-14 days of development. However, the shapes of pacemaker voltage changes do exhibit differences characteristic of cell type. Spontaneous atrial preparations rapidly depolarize from maximum diastolic potential (∼−90 mV) to a plateau range of pacemaker potentials (−80 to −75 mV). The membrane subsequently depolarizes more gradually until threshold (∼−65 mV) is reached. In contrast, spontaneously beating ventricular cell preparations slowly hyperpolarize after maximum diastolic potential to the −100 to −95 mV range before gradually depolarizing toward threshold. Voltage-clamp analysis reveals a virtual lack of any time-dependent pacemaker current in atrial preparations. These preparations are characterized by an approximately linear background current ( I) having a slope resistance of ∼100 KΩ cm. Ventricular preparations have a potassium ion pacemaker current with slow kinetics ( I), and a second time-dependent component ( I) which is activated at potentials positive to −65 mV. The background current of these preparations displays inward rectification. Computer simulations of pacemaking reveal that the initial rapid phase of pacemaker depolarization in atrial cells is determined by the membrane time constant, which is the product of membrane capacitance and the slope resistance of I. The hyperpolarization after maximum diastolic potential of ventricular cells is caused by I. The final slow phase of depolarization in both cell types is caused in part by the steady-state amplitude of the fast inward sodium current ( I). This component has negative slope conductance which effectively increases the slope resistance in the vicinity of threshold compared to TTX-treated preparations. This mechanism is sufficient to produce interbeat intervals several seconds in duration, even in the absence of time-dependent pacemaker current, provided that the background current is at the appropriate level. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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