L-type but not T-type calcium current changes during postnatal development in rabbit sinoatrial node.

Area of Science:

• Cardiovascular Physiology
• Developmental Biology
• Electrophysiology

Background:

• Neonatal sinus node exhibits a faster intrinsic rate than adult sinus node.
• Blockade of the sodium current (I(Na)) in neonatal sinus node cells results in a slower spontaneous rate compared to adult sinus node cells, indicating a potential developmental substitution of I(Na).

Purpose of the Study:

• To investigate developmental changes in calcium currents, specifically T-type calcium current (I(Ca,T)) and L-type calcium current (I(Ca,L)), in rabbit sinus node cells.
• To understand the functional role of these calcium currents in the developmental regulation of sinus node automaticity.

Main Methods:

• Utilized ruptured and perforated patch clamp techniques to record calcium currents in sinus node cells from adult and newborn rabbits.
• Analyzed current density, voltage dependence of activation and inactivation, and recovery kinetics of I(Ca,T) and I(Ca,L).

Main Results:

• I(Ca,T) density and voltage dependence remained unchanged between neonatal and adult sinus node cells.
• Adult sinus node cells displayed a lower I(Ca,L) density compared to neonatal cells.
• Significant shifts in the activation and inactivation midpoints of I(Ca,L) were observed, with adult cells showing more negative activation and less negative inactivation midpoints.
• Recovery of I(Ca,L) from inactivation was slower in neonatal cells compared to adult cells.

Conclusions:

• The developmental changes in I(Ca,L), including its reduced density, more negative activation, and faster recovery in adults, may compensate for the absence of I(Na) in adult sinus node cells.
• These alterations in I(Ca,L) contribute to the enhanced impulse initiation rate in adult sinus node cells.