Atrial natriuretic factor blocks the high-threshold Ca2+ current and increases K+ current in fetal single ventricular...

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Developmental Biology

Background:

• Atriopeptin III (ANF) is a peptide hormone known to influence cardiovascular function.
• Understanding the precise ionic mechanisms of ANF action is crucial for cardiovascular research.

Purpose of the Study:

• To investigate the effects of atriopeptin III (ANF) on specific ion currents (K+, Ca2+, Na+) in developing heart cells.
• To elucidate the role of intracellular cyclic guanosine monophosphate (cGMP) in mediating ANF's effects on cardiac ion channels.

Main Methods:

• Electrophysiological recordings (patch-clamp) were performed on single heart cells from 10-day-old chick embryos and 17- to 20-week old human fetuses.
• Specific ion currents, including high-threshold (IL) and low-threshold (IT) Ca2+ currents, fast inward Na+ current, and delayed outward K+ currents (IK), were measured.
• The impact of varying concentrations of ANF III and intracellular cGMP levels on these currents was assessed.

Main Results:

• Atriopeptin III (2 x 10(-9) M) significantly reduced high-threshold Ca2+ current (IL) but did not affect low-threshold Ca2+ current (IT) or fast inward Na+ current.
• ANF III demonstrated a dose-dependent increase in delayed outward K+ currents (IK) (10(-10) to 10(-7) M).
• The observed effects of ANF III on IK and IL were reversible, and increased intracellular cGMP selectively inhibited IL, not IK.

Conclusions:

• ANF regulates both a specific type of Ca2+ current (IL) and the delayed outward K+ current (IK) in cardiac myocytes.
• The modulation of IL by ANF may involve increased intracellular cGMP levels or other signal transduction pathways.
• ANF's differential effects on cardiac ion currents highlight its complex role in regulating heart cell electrophysiology during development.