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Biomedical subjects

S Kokubun

Publications and source records attributed to S Kokubun.

98 records · Page 6Linked to original sources
PubMed1981

Ionic mechanism underlying muscarinic acetylcholine response in the rabbit sinoatrial node.

1. The clusters composed of 10-20 cells of the rabbit sinoatrial node were prepared by coronary perfusion of collagenase and their response to ionophoretic application of ACh was recorded. The hyperpolarizing response showed a sigmoidal onset without any clear latency when the ACh pipette was positioned close to the cell surface. 2. Equations describing the kinetics and amplitude of the ACh-induced K current were determined based on the reported experimental results obtained by relaxation and noise analysis. 3. The kinetics of the ACh-induced K current simulated well the time course of the ACh response and also the effect on the spontaneous action potential when data on the kinetics was incorporated into the S-A node pacemaker mathematical model.

Acetylcholine↗
PubMed1980

The spontaneous action potential of rabbit atrioventricular node cells.

The rabbit atrioventricular (A-V) node, with dimensions of approximately 5 X 3 mm was dissected into 15 small specimens (0.5 X 0.5 mm). A majority of the specimens continued to discharge spontaneous action potentials, the action potential configuration being almost identical in different specimens. The amplitude (98 mV) and the maximum rate of rise of the action potential (11 V/sec) were similar to those recorded from the intact A-V node (amplitude 98 mV, maximum rate of rise of action potential 12 V/sec). In these small specimens, the "resting membrane potential (-44 mV)" was approximately 20 mV less negative than that in the intact A-V node preparation (-62 mV) before the dissecting procedure. The spontaneous discharge in these small A-V node specimens was attributed to the low resting membrane potential. The small specimen became inexcitable under the effects of blockers of is, though TTX had no significant effect on the action potential. The after-hyperpolarization was observed after cessation of the depolarizing current pulse. It is concluded that the slow inward current and the slow kinetics of the outward current contribute to the generation of the spontaneous A-V node action potentials as in the sinoatrial node.

Action Potentials↗
PubMedDate not supplied

Primary leiomyosarcoma with the invasion into the intertrabecular space of bone: a case report and the review of the literatures.

Primary leiomyosarcoma of bone is very rare. Most of reported cases were osteolytic. We report a primary leiomyosarcoma arising from the neck of the femur of a 43-year-old woman who had no remarkable abnormalities on plain radiographs. Magnetic resonance imaging (MRI) clearly depicted the lesion. Biopsy revealed it leiomyosarcoma. Gynecological and gastrointestinal examinations ruled out metastatic leiomyosarcoma. Wide excision of the tumor was performed and followed by endoprosthetic replacement of the proximal femur. Microscopic examination revealed tumor cells infiltrating into the intertrabecular space.

Adult↗
PubMedDate not supplied

Ca2+ channel modulation by 8-bromocyclic AMP in cultured heart cells.

Modulation of ion channels is of increasing interest as it is an important step in the regulation of cellular functions. We have analysed the effect of 8-bromocyclic AMP on Ca2+ channels in cultured cardiac cells by the patch-clamp method and report here that there was a large increase in the probability of opening of the channels. On the basis of a recently proposed kinetic reaction scheme we suggest that cyclic AMP-dependent phosphorylation of Ca2+ channels primarily promotes the forward rate constants which lead to the open state of a Ca2+ channel during depolarization.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMedDate not supplied

Muscarinic inhibition of L-type Ca2+ channels in guinea-pig tracheal smooth muscle cells.

Modulation of L-type Ca2+ channels by acetylcholine (ACh) was studied in enzymatically isolated guinea-pig tracheal smooth muscle cells (TSMCs). ACh reversibly inhibited whole cell L type Ca2+ current measured with Ba2+ ions as charge carriers (I(Ba)). With pipette solution containing 0.1 mM EGTA, 1 microM ACh induced transient inhibition of I(Ba) followed by sustained inhibition (67.0+/-3.7% of the control, n=19). When intracellular Ca2+ concentration ([Ca2+]i) was fixed at 50 nM by BAPTA-Ca2+ buffer in the pipette, the transient inhibition was abolished whereas the sustained inhibition (66.0+/-7.8%, n=6) still occurred, suggesting that the transient inhibition was attributed to inactivation of the channels induced by increase in [Ca2+]i. The sustained inhibition was abolished when [Ca2+]i was fixed at zero. The sustained inhibition of I(Ba) by 1 microM ACh was observed in the presence of 10 microM AF-DX 116, whereas it was not observed in the presence of 1 microM 4 DAMP. ACh did not inhibit I(Ba) in the presence of 1 mM GDP-beta-S in the pipette, whereas the drug irreversibly inhibited the current in the presence of 0.1 mM GTP-gamma-S in the pipette. Pretreatment of TSMCs with pertussis toxin did not altered the effects of ACh. Application of neither 1-oleoyl-2-acetyl sn-glycerol (1 microM) nor phorbol 12-myristate 13-acetate (1 microM) reduced I(Ba). These results suggest that the sustained inhibition of I(Ba) by ACh is mediated by Ca2+ requiring and protein kinase C-independent mechanisms existing in the downstream of G-protein coupled with M3 receptors.

Acetylcholine↗
PubMedDate not supplied

Vascular supply to slipped capital femoral epiphysis.

The etiology of avascular necrosis associated with slipped capital femoral epiphysis has not been well understood. The aims of this study were to clarify the blood supply to the slipped epiphysis and to examine whether this vascular supply is damaged before the reduction. Twelve patients (12 hips) underwent selective angiography of the medial circumflex femoral artery. There were seven stable slips and five unstable slips. All patients with slips underwent angiography before reduction, and one patient with an unstable slip underwent angiography both before and after reduction. The superior retinacular artery (SRA) was filled in all stable slips. This result was in accordance with the previous report that stable slips result in low rates of avascular necrosis. Of five unstable slips, the SRA was stained in two and was not filled in three. In one slip examined both before and after the manipulative reduction, the SRA was not seen before it but was well stained after it. These results have suggested that in some unstable slips the vascular injury occurs at the time of injury, before reduction, and that the reduction dose not necessarily contribute to the risk of avascular necrosis after slipped capital femoral epiphysis.

Adolescent↗
PubMedDate not supplied

Piroxicam suppositories in the treatment of osteoarthritis of the knee joint.

The subjects were 231 patients aged 16 to 75 years with osteoarthritis of the knee joint. Each patient received 20 mg of piroxicam daily as a suppository administered before sleep; 75% of the patients were treated for 14 days or longer. Overall treatment outcome was excellent in 34% according to physicians' ratings and in 36% according to the patients' self-ratings, good in 39% and 41%, fair in 22% and 17%, and unimproved in 5% and 7%, respectively. Side effects were reported by 3% of the patients. It is concluded that treatment of osteoarthritis with piroxicam suppositories is safe and effective.

Adult↗