Inward-rectifier K+ current in guinea-pig ventricular myocytes exposed to hyperosmotic solutions.

Area of Science:

• Cardiology
• Cell Physiology
• Electrophysiology

Background:

• Hyperosmotic solutions induce cell shrinkage and affect ionic currents in heart cells.
• Delayed-rectifier K+ currents are known to be inhibited by osmotic shrinkage.

Purpose of the Study:

• To investigate the effect of osmotic shrinkage on inwardly-rectifying K+ current (I(K1)) in guinea-pig ventricular myocytes.
• To determine if cell shrinkage, rather than hyperosmotic stress itself, mediates changes in I(K1).

Main Methods:

• Utilized perforated-patch and ruptured-patch electrophysiological techniques.
• Superfused ventricular myocytes with hyperosmotic Tyrode's solutions (1.3-2.2T) containing sucrose.
• Analyzed I(K1)-voltage relationships and fitted conductance-voltage data using Boltzmann functions.

Main Results:

• Hyperosmotic superfusion caused cell shrinkage, a negative shift in I(K1) reversal potential, and altered I(K1) amplitude and slope.
• Significant increases in maximal chord conductance (G(K1)max) and negative shifts in V(0.5) were observed with increasing osmolarity.
• Myocytes under non-shrinkage hyperosmotic conditions showed no significant changes in G(K1)max or V(0.5), indicating shrinkage is the key factor.

Conclusions:

• Osmotic shrinkage, not hyperosmotic stress per se, significantly alters I(K1) properties in ventricular myocytes.
• Shrinkage-induced concentration of intracellular potassium is the primary mechanism behind the observed changes in I(K1).
• Findings highlight the impact of cellular volume changes on cardiac ion channel function.