Mete ERBAŞ, ÖNER ABİDİN BALBAY, EGE GÜLEÇ BALBAY, ÖZGE UZUN, COŞKUN SILAN

Kuzu İzole pulmoner arterlerinde gelişen hipoksik pulmoner vazokonstriksiyonda Gi ve Gs proteinlerinin rolü

Hipoksik pulmoner vazokonstriksiyon akciğerlerde ventilasyon perfüzyon dengesini sağlayan fizyolojik uyum mekanizmasıdır. Hipoksemi ile seyreden progressif akciğer hastalıklarının patogenezinde önemli rol oynamakla birlikte sağlıklı bireylerde de görülmektedir. Yoğun çalışmalara rağmen, hipoksik pulmoner vazokonstriksiyonun mekanizması henüz bulunamamıştır. G proteinleri vasküler endotel ve düz kas hücrelerinde reseptör aracılıklı sinyal iletimine aracılık ederek vasküler tonusun düzenlenmesinde önemli rol oynayan membrana bağlı protein ailesidir. Biz bu çalışmada, kuzu izole pulmoner arterlerinde izlenen hipoksik vazokonstriksiyonun oluş mekanizmasında Gi ve Gs proteinlerinin rolünü saptamayı amaçladık. Pulmoner arterler yeni kesilmiş kuzuların sol akciğer alt loblarından izole edildi. Arterler Krebs-Henseleit solüsyonu ile dolu olan izole organ banyosuna asıldı ve izometrik kontraksiyonlar bilgisayarlı poligrafi sistemi ile bağlantılı olan izometrik transdüsır yoluyla devamlı olarak kaydedildi. Solüsyon %75 N2 - %20 O2 - %5 CO2 (Normoksik) ve %95 N2 - %5 CO2 (Hipoksik) karışımı içeren gazlar ile havalandırıldı. Organ banyosundaki parsiyel oksijen konsantrasyonu oksijen elektrodu kullanılarak sürekli olarak ölçüldü. Gi ve Gs proteinlerin rolünü araştırmak için kolera ve pertusis toksini kullanıldı. Çalışmada, dinlenme gerimindeki geniş çaplı pulmoner arterlerde hipoksiye bağlı bir gerim artışı izlenmedi ancak hipoksi 3 mM 5-HT ile prekontrakte edilmiş dokularda kontraksiyona (1.7±0.5 mN/mm2, n=10) sebep oldu. Hipoksik vazokonstriksiyon 2 mg/ml kolera toksini ile inkübasyon sonrası inhibe (2.6±0.4 mN/mm2den 1.0±0.4 mN/mm2ye kadar, n=6) ve 2 mg/ml pertusis toksini ile inkübasyon sonrası potansiyalize (0.6±0.4 mN/mm2den 1.7±0.3 mN/mm2ye kadar, n=6) oldu. Bu sonuçlar Gi ve Gs proteinleri ile ilişkili sinyal iletiminin geniş çaplı kuzu izole pulmoner arterinde gelişen hipoksik vazokonstriksiyonda önemli bir mekanizma olabileceğini gösterdi.

The Role of Gi and Gs Proteins in Hypoxic Vasoconstriction of Lamb Isolated Pulmonary Artery Rings

Hypoxic pulmonary vasoconstriction (HPV) is an intrapulmonary adaptive mechanism that matches alveolar ventilation to perfusion. However during prolonged alveolar hypoxia HPV occurs with many pulmonary diseases. Despite intensive studies, cellular mechanisms of HPV are still not well defined. G proteins are a family of membrane-associated proteins believed to be involved in the transduction of various signals including the regulation of vascular tonus. In this study, we aimed to determine the contribution of G i and Gs proteins in hypoxic vasoconstriction of lamb isolated pulmonary artery rings. Pulmonary arteries were isolated from left lower lobe of freshly slaughtered lamb. Arteries suspended in an organ bath filled with Krebs-Henseleit solution and isometric contraction recorded continuously via an isometric transducer connected to a computerised polygraphy system. The solution aerated with 75% N2 - 20% O2 - 5% CO2 (normoxic) and 95% N2 - 5% CO2 (hypoxic) pO2 of bathing medium was measured continuosly using an oxygen electrode. Pertussis toxin and cholera toxin were used to investigate the role of Gi and Gs proteins. In the present study, we observed that hypoxia had no effect on resting force in large artery rings, but it caused a further contraction (1.7±0.5 mN/mm2, n=10) in 3 mM 5-HT precontracted pulmonary arteries rings. Hypoxic vasoconstriction was inhibited by preincubation with 2 mg/ml cholera toxins (from 2.6±0.4 mN/mm 2, to 1.0±0.4 mN/mm2, n=6) and potentiated by preincubation with pertussis toxins (2 mg/ml) (from 0.6 ± 0.4 mN/mm2, to 1.7±0.3 mN/mm2, n=6). These results indicate that signal transduction mediated by Gi and Gs proteins may be an important mechanism in the hypoxic vasoconstriction in lamb isolated large pulmonary arteries.

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