Characterization of a TTX-sensitive Na+ current in pacemaker cells isolated from rabbit sinoatrial node

Abstract

A tetrodotoxin (TTX)-sensitive Na+ current (iNa) was investigated in single pacemaker cells after 1-4 days in culture. Ruptured-patch and perforated-patch whole cell recording techniques were used to record iNa and spontaneous electrical activity, respectively. For seven cells exposed to 20 mM Na+ (22-24 degrees C) and held at -98 mV (25% of the channels inactivated), the uncorrected maximum iNa was -39 +/- 10 pA/pF at -29.1 +/- 2.4 (SE) mV, maximum conductance was 0.9 +/- 0.2 nS/pF (1.6 +/- 0.2 mS/cm2). Half-activation and inactivation potentials were -41.4 +/- 2.0 and -90.6 +/- 2.5 mV, and the corresponding slope factors were 6.0 +/- 0.4 and 6.4 +/- 0.6 mV. Inactivation and recovery from inactivation were best fit by sums of two exponentials. During action potential clamp, a TTX-sensitive compensation current accounted for 55% of the upstroke velocity. The results suggest that iNa contributes significantly to the action potential in some nodal pacemaker cells, and the characteristics of iNa are similar to those of atrial and ventricular myocytes.

Culture and adenoviral infection of sinoatrial node myocytes from adult mice

“…Although it would be preferable to avoid the use of BDM, we found it to be an essential component of our SAM culture protocol; we attempted numerous cultures in the absence of BDM, but in each case, the number of spindle-shaped spontaneously active cells was dramatically reduced, and no such cells were observed beyond 24 h in vitro (not shown). These observations are consistent with previous reports in which adult rabbit SAMs cultured in the absence of BDM tended to round-up and dedifferentiate (21,29,44).…”

“…In addition, I f is expressed in only about one-third of HL-1 cells (45) (when compared with 100% of the cultured SAMs in the present study) and appears to be produced primarily by the HCN1 and HCN2 isoforms (35) (rather than HCN4, which is the predominant isoform in SAMs) (28). Although primary cultures of SAMs from adult rabbits have been reported, the cultured cells exhibited significant morphological dedifferentiation (21,29,44) and fired spontaneous APs at a rate at least 50% slower than observed in acutely isolated cells.…”

An unexpected role for brain-type sodium channels in coupling of cell surface depolarization to contraction in the heart

“…Because no reduction was observed, this represents an upper limit on the percentage of current due to TTX-sensitive isoforms. Thus, despite showing the presence of TTX-sensitive sodium channels using ␤ scorpion toxin, our results parallel previous findings reporting an EC 50 for TTX in the micromolar range in cardiac preparations and failing to detect a high-affinity population of sodium channels (19,25,29,30).…”

Clinical Aspects and Prognosis of Brugada Syndrome in Children

“…29 -31 Although the role of I Na in the sinus node has been debated, it is now well established that sodium channels contribute to sinus node pacemaking in mammals. 32,33 In the population described here, the proportion of patients carrying a SCN5A mutation is far higher than usually described in BrS (20% to 30%). This finding can be explained by the following explanations.…”