Differences in the expression pattern of HCN isoforms among mammalian tissues: sources and implications

Area of Science:

• Molecular Biology
• Cell Physiology
• Neuroscience

Background:

• Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are crucial in various cell types.
• The expression patterns of different HCN isoforms are not well understood across tissues.

Purpose of the Study:

• To compare the expression of HCN isoforms (HCN1-4) in rat excitable and non-excitable tissues at mRNA and protein levels.
• To investigate the correlation between mRNA and protein expression for HCN isoforms.
• To explore post-translational modifications influencing HCN channel expression.

Main Methods:

• Real-time PCR for mRNA expression analysis.
• Western blot analysis for protein expression assessment.
• Comparison of theoretical and electrophoretic molecular weights.

Main Results:

• Distinct mRNA and protein expression patterns for HCN isoforms were observed in brain, heart, pituitary, and kidney.
• HCN2 was the most abundant mRNA in kidney, heart, and pituitary, while HCN4 was most abundant in brain.
• HCN4 was the predominant protein isoform across tissues, with significant variations in isoform stoichiometry.
• Deviations in molecular weight suggested N-glycosylation and proteolysis impact HCN channel expression.

Conclusions:

• HCN channel expression is isoform-specific and tissue-dependent, with complex mRNA-protein correlations.
• HCN4 is a major contributor to HCN channel protein in heart and other tissues.
• Post-translational modifications like N-glycosylation and enzymatic cleavage likely modulate HCN channel function and surface expression.