# Tribute to Alberto J. Kaumann

## TL;DR

This paper honors Alberto J. Kaumann's scientific legacy, focusing on his work in cardiovascular adrenergic and serotonergic systems and his key discoveries in receptor subtypes and drug effects.

## Contribution

Kaumann's classification of β-adrenoceptor subtypes and elucidation of serotonin's direct cardiac effects represent novel contributions to cardiovascular pharmacology.

## Key findings

- Kaumann classified cardiac β-adrenoceptors into β1- and β2-AR using subtype-selective antagonists.
- He demonstrated that β2-AR dual coupling to Gαs- and Gαi-proteins has minor role in healthy hearts.
- He showed serotonin's positive inotropic effect is via 5-HT receptor activation, not noradrenaline release.

## Abstract

This review summarises the major contributions of Alberto J. Kaumann who died in December 2024. The German-born pharmacologist devoted his scientific life to the cardiovascular adrenergic and serotinergic systems. He classified the subtypes of the cardiac β-adrenoceptors (β-AR) into β1- and β2-AR using the subtype-selective antagonist. In addition, he showed that the dual coupling of β2-AR to Gαs- and Gαi-proteins plays a minor role in the healthy heart. He also found that the positive inotropic effect of serotonin (5-HT) was not mediated by release of noradrenaline, but due to activation of a specific 5-HT receptor coupled to Gαs-proteins. His experiments with prostaglandin-E1 demonstrated an increase in cAMP and spontaneous beating frequency of the heart in the absence of a positive inotropic effect, suggesting a compartmentation of cAMP. This finding was later verified by experiments with subtype-selective phosphodiesterase inhibitors. Last not least, he explained the antiarrhythmic effect of sotalol by prolongation of the cardiac action potential duration, providing for the first time, what was years later to be defined as class III antiarrhythmic action. With Alberto Kaumann, we have lost a colleague and friend who had dedicated his life to science and music.