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Published on: March 12, 2013
Effect of isoprenaline on I(f) current in latent pacemaker cells isolated from cat right atrium: ruptured vs.
1Loyola University Medical Center, Department of Physiology, Maywood, IL 60153.
Insights
The recording method significantly impacts studying the hyperpolarization-activated current (I(f)) in atrial pacemaker cells. The nystatin-perforated-patch method preserves I(f) function, allowing isoprenaline to consistently increase current and heart rate.
Area of Science:
- Cardiology
- Electrophysiology
- Cellular Physiology
Background:
- The hyperpolarization-activated current (I(f)) is crucial for pacemaker activity in the heart.
- Investigating I(f) in latent atrial pacemaker cells requires robust experimental techniques.
- The influence of recording methods on cellular function and drug response is a critical consideration.
Purpose of the Study:
- To investigate the functional properties of the hyperpolarization-activated current (I(f)) in latent atrial pacemaker cells.
- To determine the effect of isoprenaline on I(f) and pacemaker activity.
- To compare the efficacy of standard ruptured-patch versus nystatin-perforated-patch whole-cell recording methods for studying I(f).
Main Methods:
- Whole-cell recording techniques (ruptured-patch and nystatin-perforated-patch) were employed on isolated cat right atrial latent pacemaker cells.
- Time-dependent inward current activated on hyperpolarization (I(f)) was measured.
- The effects of isoprenaline on I(f) amplitude, activation kinetics, and spontaneous beating rate were analyzed.
Main Results:
- The ruptured-patch method led to a significant "run-down" of I(f) amplitude and variable responses to isoprenaline.
- The nystatin-perforated-patch method maintained I(f) stability and revealed consistent effects of isoprenaline.
- Isoprenaline significantly increased I(f) amplitude by 90% and accelerated the spontaneous rate by 58%, shifting the activation curve positively by 11 mV using the perforated-patch method.
Conclusions:
- Latent atrial pacemaker cells consistently exhibit functional I(f) current.
- The nystatin-perforated-patch method is superior for preserving I(f) function and assessing isoprenaline's effects.
- Isoprenaline reliably enhances I(f) amplitude and pacemaker activity in latent atrial pacemaker cells.
Abstract:
Whole-cell recording techniques were used to study the time-dependent inward current activated on hyperpolarization (I(f)) and its response to isoprenaline in latent atrial pacemaker cells isolated from cat right atrium. To determine whether the response to isoprenaline depended on the type of recording method, we analysed I(f) using either a standard ruptured-patch, or a nystatin-perforated-patch, whole-cell recording method. All cells beat rhythmically at 35 degrees C and exhibited normal pacemaker action potentials and I(f) current, regardless of the recording method. With the ruptured-patch method, pacemaker action potentials ceased activity within a few minutes and I(f) amplitude decreased "ran down" to 74% of control within 10 min of rupturing the patch. Isoprenaline (1 microM) elicited variable changes in I(f) amplitude among different latent pacemaker cells resulting in no net change in mean current amplitude (n = 6). In addition, isoprenaline failed to change the voltage dependence of the I(f) activation curve. On the other hand, using a nystatin-perforated-patch method, pacemaker action potentials and I(f) exhibited no significant changes over the same 10 min period. Under these conditions, isoprenaline consistently increased I(f) in all cells studied (+90%) at -80 mV; n = 8), and increased the spontaneous rate of pacemaker action potentials by 58 +/- 7% (n = 5). Moreover, isoprenaline elicited a significant positive shift (+11 mV) in the half-maximal activation voltage of the I(f) activation curve (n = 3). We conclude that latent atrial pacemakers consistently exhibit I(f) current, and that isoprenaline consistently elicits an increase in I(f) amplitude.(ABSTRACT TRUNCATED AT 250 WORDS)
