Verapamil blocks basolateral K+ channels in the larval frog skin

Area of Science:

• Physiology
• Membrane Transport
• Pharmacology

Background:

• Short-circuit current (Isc) measurements are crucial for studying ion transport across epithelial tissues.
• Potassium (K+) channels play a vital role in regulating membrane potential and ion flux.
• Understanding ion channel modulation is key to comprehending physiological processes and developing therapeutic strategies.

Purpose of the Study:

• To investigate the inhibitory effects of verapamil on K+ channels in isolated larval frog skin.
• To characterize the kinetics and mechanism of verapamil-induced inhibition of short-circuit current (Isc).
• To elucidate the components involved in K+ channel blockade in the basolateral membrane.

Main Methods:

• Measurement of short-circuit current (Isc) across isolated frog skin (Rana catesbeiana) under varying Ringer solution conditions.
• Application of nystatin to enhance mucosal K+ permeability.
• Dose-dependent inhibition of Isc using verapamil.
• Kinetic analysis using direct linear plot and fluctuation analysis.

Main Results:

• Nystatin addition significantly increased Isc, confirming K+ permeability.
• Verapamil progressively inhibited Isc in a dose-dependent manner, with significant reduction at 80 microM.
• Kinetic analysis indicated pseudo-first-order kinetics for Isc blockage with a Michaelis constant (Km) of 9.59 microM.
• Fluctuation analysis revealed a Lorentzian component, suggesting verapamil interacts with K+ channels, decreasing single-channel currents.

Conclusions:

• Verapamil exhibits a dose-dependent inhibition of K+ channels in the basolateral membrane of larval frog skin.
• The inhibition mechanism appears to involve at least two components.
• Kinetic and fluctuation analyses provide insights into the interaction of verapamil with K+ channels, affecting both channel activity and kinetics.