ABSTRACT
BACKGROUND: In the sinoatrial node (SAN) the course of the action potential gradually changes from the primary pacemaker region toward the atrium. It is not known whether this gradient results from different intrinsic characteristics of the nodal cells, from an increasing electrotonic interaction with the atrium, or from both. Therefore we have characterized the immunohistochemical, morphological, and electrophysiological correlates of this functional gradient. METHODS AND RESULTS: The distribution of rabbit nodal myocytes in the SAN has been studied by immunohistochemistry. After cell isolation, the electrophysiological characteristics of different nodal cell types were measured. (1) The staining pattern of a neurofilament protein coincides with the electrophysiologically mapped pacemaker region in the SAN. (2) Enzymatic digestion of the SAN reveals three morphologically different nodal cell types and one atrial type. Of each nodal cell type, neurofilament-positive as well as neurofilament-negative myocytes are found. Atrial cells are all neurofilament-negative. (3) In contrast to previous findings, we observed atrial cells in the very center of the SAN. The relative number of atrial cells gradually increases from the central pacemaker area toward the atrium. (4) Differences in electrophysiological characteristics between individual nodal cells are not associated with differences in cell type. CONCLUSIONS: (1) The expression of neurofilaments can be used to delineate the nodal area in the intact SAN but is not sufficiently sensitive for characterizing all individual isolated nodal cells. (2) A fundamentally different organization of the SAN is presented: The gradual increase in density of atrial cells from the dominant area toward the crista terminalis in the SAN causes a gradual increase of atrial electrotonic influence that may be an important cause of the gradual transition of the nodal to the atrial type of action potential.
Subject(s)
Atrial Function , Heart Atria/cytology , Sinoatrial Node/cytology , Sinoatrial Node/physiology , Action Potentials , Animals , Cell Differentiation/physiology , Neurofilament Proteins/physiology , RabbitsABSTRACT
The role of the delayed rectifier current (IK) in impulse generation was studied in single sinoatrial nodal myocytes of the rabbit. We used the class III antiarrhythmic drug E-4031, which blocks IK in rabbit ventricular myocytes. In single sinoatrial nodal cells, E-4031 (0.1 mumol/L) significantly prolonged cycle length and action potential duration, depolarized maximum diastolic potential, and reduced both the upstroke velocity of the action potential and the diastolic depolarization rate. Half of the cells were arrested completely. At higher concentrations (1 and 10 mumol/L), spontaneous activity ceased in all cells. Three ionic currents fundamental for pacemaking, ie, IK, the long-lasting inward calcium current (ICa,L), and the hyperpolarization-activated current (I(f)), were studied by using the whole-cell and amphotericin-perforated patch technique. E-4031 blocked part of the outward current during depolarizing steps as well as the tail current upon subsequent repolarization (ITD) in a dose-dependent manner. E-4031 (10 mumol/L) depressed ITD (88 +/- 4%) (n = 6), reduced peak ICa,L at 0 mV (29 +/- 15%) (n = 4), but did not affect I(f). Lower concentrations did not affect ICa,L. Additional use of 5 mumol/L nifedipine demonstrated that ITD is carried in part by a calcium-sensitive current. Interestingly, complete blockade of IK and ICa,L unmasked the presence of a background current component with a reversal potential of -32 +/- 5.4 mV (n = 8) and a conductance of 39.5 +/- 5.6 pS/pF, which therefore can contribute both to the initial part of repolarization and to full diastolic depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)
Subject(s)
Anti-Arrhythmia Agents/pharmacology , Piperidines/pharmacology , Pyridines/pharmacology , Sinoatrial Node/drug effects , Sinoatrial Node/physiology , Action Potentials , Animals , Calcium/physiology , Diastole , Electrophysiology , Female , In Vitro Techniques , Male , Membrane Potentials , Nifedipine/pharmacology , Patch-Clamp Techniques , Rabbits , Sinoatrial Node/cytologySubject(s)
Breast Neoplasms/diagnosis , Biopsy, Needle , Breast Neoplasms/pathology , Breast Neoplasms/surgery , Female , HumansABSTRACT
Based upon the principles of the standard photographic reconstruction method (Los, 1970/71) a quicker method is achieved. While formerly the cut-out structures were thickened afterwards with board, the photographs are now stuck to polystyrene sheets before cutting. Cutting is done with an electric soldering iron fitted with a double-edged cutting knife. This technique permits the cutting out of small structures and is quick, simple and inexpensive. Finally, it has the advantages of speeding up the reconstruction procedure.
